1. Field of the Invention
The present invention relates to a positioning device for fitting implant-supported dental prostheses.
2. Description of the Related Art
The concept of implanting artificial roots to replace missing teeth or as abutments for prostheses is known. The dental implants, generally made of titanium, are screwed into the jawbone where, after osseointegration, that is to say “healing” of the bone around the implant, they will serve as stable abutments on which the future prosthetic restorations (crowns, bridges or dentures) will be fixed.
In a patient without any teeth, when the local anatomical conditions are respected, creating a complete bridge supported by implants represents the best alternative to a removable total prosthesis, both from the point of view of comfort and also from the point of view of mastication function or esthetics.
The durability of the implant depends directly on the quality of its connection to the bone in which it is inserted, to obtain sufficient osseointegration, a waiting period of 2 to 6 months, during which the implant must remain protected from any damaging mechanical stress, is generally necessary between the time it is fitted and the time it is loaded.
Paradoxically, it has now been clearly demonstrated that loading of implants on the same day they are inserted (immediate loading) is possible, for example in the case of restoration of toothless jaws with the aid of rigid structures such as complete bridges, without significantly compromising their long-term viability. The reason for this particular feature lies in better stabilization of the individual implants and more uniform distribution of the mechanical stresses by the rigid structure of the complete bridge, not compromising the phenomenon of osseointegration.
However, the creation of a complete bridge supported by implants poses numerous technical problems associated with their correct insertion. Besides the fact that they have to be inserted at precise locations, they also have to be inserted on a strictly parallel axis permitting postoperative insertion of the bridge.
For this reason, the surgical phase is first of all preceded by what is known as a planning phase during which the future prosthesis is made of wax for diagnostic purposes on casts of the patient's jaws. This makes it possible in particular to decide on the number, position and axis of insertion of the future implants. To ensure a logical continuity between this preliminary step and the surgical phase, it is essential to use a transfer device when fitting the implants: the surgical guide. The latter is in the form of a transparent acrylic resin replica of the future prosthetic restoration. Placed in the mouth, on the toothless gum, it is equipped with parallel wells serving for drilling the implant beds at predetermined locations in the jawbone.
Its use is crucial in cases of restoration of toothless jawbones with complete bridges, accompanied by immediate loading, where postoperative insertion of the temporary bridge is possible only if the implants are placed in a strictly parallel arrangement. Moreover, two other parameters must also be respected in such a situation in order to permit correct occlusion (or meshing) of the bridge with the antagonist teeth: the vertical dimension of occlusion (VDO) and the intermaxillary relationship (IMR). The VDO represents the height of the lower region of the face delimited by the lower margin of the nose and the lower margin of the chin. The IMR represents, in the horizontal plane, the position of the lower jaw relative to the upper jaw.
These three references are established, in the subject completely without teeth, either by the morphology of his/her existing prosthesis (prostheses) or by the diagnostic fitting of the teeth during the preliminary phase. It is imperative that these parameters are transposed to the future bridge which will be placed in the mouth as soon as the final implants have been inserted. Failing to do so leads to problems with occlusion of the teeth and to various clinical manifestations (pain, muscle fatigue, poor mastication, etc.) which are generally not tolerated by the patient.
Hitherto, only surgical guides resting on the toothless gum have been used for implant restoration of toothless jaws. Such restorations generally necessitate incision and reclination of a large surface of the gum, thus compromising the peroperative stability of the surgical guide on the mucous support. Moreover, there is presently no method of reliably recording and plotting the VDO and IMR before the operation to permit precise adaptation of the temporary bridge according to these criteria.
The object of the present invention is to remedy this situation at least in part.